PROBLEM TO BE SOLVED: To provide a one-component water treatment agent composition in which troubles due to microbes, scale and corrosion in various water systems can be prevented； blended combined bromine compounds are little in decomposition even under high-temperature environment； and a storage stability is improved.SOLUTION: A water treatment agent composition in a water system includes as effective components, (A) a combined bromine compound obtained by reaction of hypobromous acid and/or hypobromite with sulfamic acid and/or sulfamate, and (B) at least one selected from (1) a telomer obtained by reaction of a telogen selected from sulfurous acid, water-soluble sulfite and amine thiol with an unsaturated monomer having no hydroxyl group, (2) an organic phosphinic acid compound obtained by reaction of hypophosphorous acid and/or water-soluble hypophosphite with the unsaturated monomer having no hydroxyl group, and (3) an organic phosphonic acid compound having no hydroxyl or amino group. The pH of the composition is made to be 13 or higher.SELECTED DRAWING: None【課題】各種水系における微生物障害、スケール障害及び腐食障害を抑制でき、高温度環境下においても配合された結合臭素化合物の分解が少なく、貯蔵安定性が改善された一液の水処理剤組成物の提供。【解決手段】（Ａ）次亜臭素酸及び／又は次亜臭素酸塩とスルファミン酸及び／又はスルファミン酸塩の反応により得られる結合臭素化合物と、（Ｂ）（１）亜硫酸、水溶性亜硫酸塩及びアミンチオールから選択されるテロゲンとヒドロキシル基を有さない不飽和単量体の反応で得られるテロマー、（２）次亜リン酸及び／又は水溶性次亜リン酸塩とヒドロキシル基を有さない不飽和単量体との反応で得られる有機ホスフィン酸化合物、及び（３）ヒドロキシル基及びアミノ基を有さない有機ホスホン酸化合物から選択される１種以上とを、有効成分として含み、組成物のｐＨを１３以上とする、水系における水処理剤組成物。【選択図】なし
